Segregation dynamics of a Pd-Ag surface during CO oxidation investigated by NAP-XPS

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Segregation dynamics of a Pd-Ag surface during CO oxidation investigated by NAP-XPS. / Strømsheim, Marie D.; Svenum, Ingeborg Helene; Mahmoodinia, Mehdi; Boix, Virgínia; Knudsen, Jan; Venvik, Hilde J.

I: Catalysis Today, 2021.

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

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Strømsheim, Marie D. ; Svenum, Ingeborg Helene ; Mahmoodinia, Mehdi ; Boix, Virgínia ; Knudsen, Jan ; Venvik, Hilde J. / Segregation dynamics of a Pd-Ag surface during CO oxidation investigated by NAP-XPS. I: Catalysis Today. 2021.

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TY - JOUR

T1 - Segregation dynamics of a Pd-Ag surface during CO oxidation investigated by NAP-XPS

AU - Strømsheim, Marie D.

AU - Svenum, Ingeborg Helene

AU - Mahmoodinia, Mehdi

AU - Boix, Virgínia

AU - Knudsen, Jan

AU - Venvik, Hilde J.

PY - 2021

Y1 - 2021

N2 - The dynamic changes in composition in the near-surface region of a Pd75%Ag25%(100) single crystal were monitored using near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) during CO oxidation under oxygen rich conditions at a total pressure of 1.1 mbar. Six CO oxidation temperature cycles were investigated at different heating rates and maximum temperatures of 450 °C or 600 °C. It was found that the history of the bimetallic sample plays an important role, as the CO2 formation profile varies depending on initial conditions, and previous heating rates and maximum temperatures. In terms of CO coverage effects, normal, reversed and no hysteresis behaviour were all observed. In agreement with previous modelling predictions, the NAP-XPS data confirm a dynamic segregation behaviour upon heating/cooling where the amount of Pd in the surface region decreases with increasing temperature. Nevertheless, the Pd 3d5/2 core level relative area assessment is not fully capable of capturing all the surface dynamics inferred from the temperature dependent CO2 formation profiles, due to the probing depth. While residing at ambient temperature in the reaction mixture, however, there is a build-up of adsorbed CO at the surface showing that CO induces segregation of Pd to the topmost surface layer under these conditions. In total, this suggests that the segregation is kinetically relatively facile during temperature cycling, and that adsorbate coverage is the main controlling factor for the surface termination.

AB - The dynamic changes in composition in the near-surface region of a Pd75%Ag25%(100) single crystal were monitored using near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) during CO oxidation under oxygen rich conditions at a total pressure of 1.1 mbar. Six CO oxidation temperature cycles were investigated at different heating rates and maximum temperatures of 450 °C or 600 °C. It was found that the history of the bimetallic sample plays an important role, as the CO2 formation profile varies depending on initial conditions, and previous heating rates and maximum temperatures. In terms of CO coverage effects, normal, reversed and no hysteresis behaviour were all observed. In agreement with previous modelling predictions, the NAP-XPS data confirm a dynamic segregation behaviour upon heating/cooling where the amount of Pd in the surface region decreases with increasing temperature. Nevertheless, the Pd 3d5/2 core level relative area assessment is not fully capable of capturing all the surface dynamics inferred from the temperature dependent CO2 formation profiles, due to the probing depth. While residing at ambient temperature in the reaction mixture, however, there is a build-up of adsorbed CO at the surface showing that CO induces segregation of Pd to the topmost surface layer under these conditions. In total, this suggests that the segregation is kinetically relatively facile during temperature cycling, and that adsorbate coverage is the main controlling factor for the surface termination.

KW - Bimetallic catalysis

KW - Carbon monoxide oxidation

KW - Palladium

KW - Segregation

KW - Silver

KW - Single crystal surface

U2 - 10.1016/j.cattod.2021.02.007

DO - 10.1016/j.cattod.2021.02.007

M3 - Article

AN - SCOPUS:85102300997

JO - Catalysis Today

JF - Catalysis Today

SN - 0920-5861

ER -